The present invention relates to a drive assembly for arrangement thereof between a drive-input unit, a drive output unit, and a transmission unit.
Such an assembly is known from European patent application EP-A-0.127.986. In this known construction the drive unit is composed by a combustion engine and the load by the vehicle, driven via one or more wheels thereof. In the known assembly the transmission is continuously variable, and a flywheel is arranged to be selected at driving off conditions for fuel economy. The known construction hereto requires clutches and controls for selecting there between, rendering the construction relatively expensive and complicated.
It is in automotive engineering an ongoing issue to reduce energy consumption at use of the vehicle. One way of achieving this is to minimise the size of the drive unit. This reduces weight to be moved and provides an optimal use of the drive unit and, at combustion engines, usually provides better combustion efficiency. A disadvantage of so-called small drive units is the bad load response, i.e. its unfavourable acceleration delay, due to necessary engine speed up. The present invention aims amongst others at favourably enabling the application of such drive units.
A known drive assembly used in co-operation with small drive units is embodied by the so-called Integrated Motor Assist system as commercialised by Honda. It comprises an electrical motor coupled in series with a continuously variable transmission between a drive unit composed by a combustion engine and a load composed by a drive axle of the vehicle. The problem of insufficient acceleration response is in this construction solved through the presence of an electrical accumulator providing additional power at acceleration, thus assisting the combustion engine. The battery is fed by the engine during less requiring operating conditions (and/or by absorbing braking energy). The known drive assembly is advantageous in that due to the presence of the accumulator the internal combustion engine can be chosen to be one with relatively low maximum engine torque, usually a relatively small engine. Disadvantages of the known construction relate to the use of, and the conversion of kinetic energy into electrical energy and the weight and cost of the electrical installation.
It is the object of the present invention to provide a drive assembly enabling the utilisation of energy saving, relatively light drive units while maintaining the advantage of utilising conventional i.e. mechanical technology and while keeping costs and weight of the assembly down. According to the invention this can be achieved by applying a construction as described in the characterising portion of claim 1. In the construction according to the invention an epicyclic gearing know per se is utilised. This is done in such a manner that a rotational member may, alternating in time, operate as an output member and as an input member. Also, one rotational member is provided with a flywheel function i.e. it is provided as a flywheel or operatively connected therewith. A desired ratio between two of the rotational members of the gearing is realised by a transmission operatively connecting two members. In such arrangement the kinetic energy absorbed by the flywheel during drive conditions will be released in either or both directions of the drive unit and load during acceleration of the drive unit, thereby assisting the drive unit. The construction is favourable in that it uses conventional technology with readily available components in a relatively simple configuration, while the weight of the flywheel to be used may be kept relatively low. Also, the construction may be used in combination with any of the known types of transmission.
It is remarked that drivelines utilising a flywheel as a kinematic accumulator are known per se. They are applied in a manner enabling the drive of the vehicle only, rather than being capable of assisting the engine as according to the invention. In a usual configuration such flywheel is in parallel coupled to an input shaft of a transmission, parallel to a drive unit, such that drive unit and flywheel may alternatively operate as a power source for driving the load. Since the flywheel is only capable of unloading energy when slowing down it can not be used to assist an engine in raising its rotational speed as intended by the invention.
It is further remarked that the use of epicyclic gearing for automotive transmission, in particular planetary stages, is generally known. The purposes of utilisation differ from that of the present invention in that they are normally applied as a transmission for improvement of the efficiency of a continuously variable transmission used in combination herewith or to change the ratio coverage of a transmission applied in combination herewith. In the construction known from international patent application WO 96/35063 a planetary stage is provided operatively between engine and load, and a continuously variable transmission is arranged between the pinion carrier thereof and either the sun or the ring gear. In this construction the carrier is connected to the engine and the sun is connected to the vehicle. It is in the art also known that epicyclic gearings may be used to increase the overall transmission efficiency while reducing the ratio coverage or, vice versa, to increase ratio coverage to the detriment of the overall transmission efficiency. It is further remarked that the use in parallel of a planetary stage and a CVT between an input unit and an output unit, each being one of three inertia components is known per se. European patent publication EP-A-0.058.720 discloses a stand by energy source having such arrangement and indicated to be intended for equipment in which energy must be supplied absolutely continuously. The known arrangement differs from the present construction in that the automotive application primarily deals with the dynamic interaction between three moving inertia components while in use, in particular during vehicle acceleration as may be desired or necessary in traffic conditions. The present invention in particular differs from the known arrangement in that it teaches how to use a light weight efficiently operating engine for a vehicle without detrimental effect to the drivability of the vehicle.